1. Field of the Invention
The present invention pertains to an emergency release valve apparatus mainly for use in a marine loading arm installation for transferring fluid products.
2. Prior Art
A marine loading arm installation is conventionally employed for unloading petroleum products from a tank vessel to a storage tank on land or for loading the same from the storage tank to the tank vessel. The loading arm installation includes an assembly of articulated pipe sections carrying a flanged end connector and is mounted on a sea berth for bolted connection of the end connector to a similar flanged connector on the manifold of the tank vessel. During the transfer of the fluid cargo, the vessel moves due to wind, tide or wave, and the level of the deck thereof changes. Then, the pivotal arms of the loading arm installation can move following the movement of the vessel. However, an excessive movement of the vessel may cause the intervening space between the vessel and the sea berth to exceed the safety reach of the loading arm. In such a case, since the bolted connection of the loading arm to the manifold is unyielding, one of the pipe sections or other parts of the loading arm will break. Consequently, in the conventional loading arm, in order to prevent the breakage and a serious hazard in that case, an emergency release valve apparatus as shown in FIGS. 1 to 3 of the accompanying drawings is mounted on the loading arm adjacent to the end connector thereof.
The prior art emergency release valve apparatus, generally indicated at 200, includes a pair of shut-off valves 202 comprising, for example, ball valves disposed between the flanged ends of the pipes (not shown) and secured thereto, respectively, drive means 204 for closing the two valves 202 as soon as an emergency arises, and a coupling device 206 which couples the two valves 202 together in ordinary loading or unloading conditions and uncouples them the moment the two valves 202 are closed. The drive means 204 includes a drive hydraulic cylinder 208 operable to rotate stems 202a of the two valves 202 through a link assembly 210 to close simultaneously the two valves 202 in case of emergency. The coupling device 206 includes a plurality of clamping members 212 disposed to straddle opposed inner flanges 202b of the two valves 202 to be coupled, a plurality of connecting rods 214 hinged at their ends to respective pairs of clamping members 212 so as to form an articulated succession of the clamping members 212, the clamping members 212 and the connecting rods 214 being disposed around the inner flanges 202b in the form of a ring provided with a gap between two end clamping members 212, and connecting means 216 having a connecting hydraulic cylinder 216a for releasably coupling the two end clamping members 212 to complete the ring. Thus, in the loading arm installation, when an emergency arises, conventional control means senses the emergency and actuates the drive hydraulic cylinder 208 of the drive means 204 to close the two valves 202, and subsequently actuates the connecting means 216 of the coupling device 206 to uncouple the two valves 202 to disconnect the two pipes.
However, the prior art valve apparatus is excessively heavy as well as intricate in structure since it includes the two valves 202 which are heavy by themselves and the link assembly 210 for driving the two valves 202 with one cylinder 208. Inasmuch as the emergency release valve apparatus is mounted on the loading arm adjacent to the end connector thereof, and is heavy, a large dynamic load is exerted on the pipe sections of the loading arm and a frame for supporting the pipe sections so that great strength is required for the pipe sections and the frame. In addition, in the prior art valve apparatus described above, when the two valves 202 are closed, fluid remains in a vacancy 218 formed between the two valves 202. Therefore, the remaining fluid is scattered during the disconnection of the two valves 202. This is very dangerous in the case where combustible or poisonous fluid cargo is transferred through the loading arm installation. Further, there is sometimes a case where the two valves 202 are kept coupled together for a while after they are closed. In such a case, when very low temperature fluid cargo such as liquefied natural gas is transferred through the loading arm, the pressure of the remaining fluid in the vacancy 218 is increased due to a rise of temperature to cause damage to the valves 202 or the leakage of the fluid.